1. Field of the Invention
The present invention relates in general to communication systems, and relates in particular to a mobile telephone communication apparatus which can be used as a child phone of a cordless home phone in a certain service area as well as a car phone or a portable phone in another service area, and a method using the apparatus.
2. Technical Background
Mobile communication through a public fixed communication network, such as portable telephones or car phones, have assumed increasing importance as a way of personal and business communications.
For example, mobile telephone communications are essential in business activities, and it is often necessary for a businessman with car phones and/or portable phones to make communication from outside of the office. Also, in the office, fixed terminal devices such as cordless home phones are provided, and it is desired to use such a car phone or a portable phone as a child phone of a cordless home phone in the office.
First, a method of accessing a mobile terminal device in the conventional mobile communication system will be explained. FIG. 1 illustrates an example of a configuration for mobile communication system connected to the public fixed communication network. A fixed terminal device 2 within the public fixed communication network (N-terminal fixed device, for short) 1, a fixed terminal device 61 for the mobile communication system (M-terminal fixed device, for short), and a terminal device switching means 3 are connected to the public fixed communication network 1, and communicate with each other through the public fixed communication network 1. The terminal device switching means 3 has a data base 4 and provides switching services for calls relating to a first service area 5, comprising base stations 50-52. The terminal device switching means 3 performs switching operations for a first portable device 8 and for a mobile terminal device 53 within the first service area 5 in accordance with the information in the data base 4. The base stations 50-52 provide radio communications with the first portable device 8 and with the mobile terminal device 53 within the first service area 5. The terminal devices 8, 53 act as a subscriber terminal of the terminal device switching means 3. The M-terminal fixed device 61 performs radio communications with a child device (second portable device) 62 located within the second service area 6. The mobile terminal device 53 and the child device 62 are utilized by the mobile terminal user 7 (user 7 for short) who is a subscriber to the mobile communication system.
The car phone system and the cordless home telephone system indicated in FIG. 1 represent typical examples of devices in such a mobile communication system. In this case, the terminal device switching means 3 corresponds to a car phone switching device; the mobile terminal device 53 to a car phone; and the M-terminal fixed device 61 to a cordless mother phone; and the child device 62 corresponds to the child device of the cordless mother phone.
In general, because car phone and cordless phone systems operate on different carrier frequencies and communications protocals, when the user 7 does not use the N-terminal fixed device 2 of the public fixed communication network 1, the user 7 must use the two different types of mobile terminal devices, first portable device 8 or the second portable device 61, mentioned above. When the N-terminal fixed device 2 tries to access the mobile terminal device (car phone) 53 by specifying the subscriber number, and if the location information of the mobile terminal device (car phone) 53 has a registered access area including the base station 52, the call sequence is as shown in FIG. 7. If the user 7 has moved into the second service area 6, the user 7 (the subscriber) is unable to respond to the call. Currently this problem is resolved by providing a call transfer as an optional service for the subscriber number assigned to the mobile terminal device (car phone) 53. As shown in FIG. 6, the data base 4 for the subscribers, N(0) to N(n), includes an optional service information and a location information. For the case of the subscriber N(0), there is no call forward service, and the subscriber does not receive any forwarded calls. For the subscriber N(n), the optional service information contains the subscriber number of the M-terminal fixed device (cordless mother phone) 61 as the call forward telephone number, then as shown in FIG. 8, the call can be forwarded to the M-terminal fixed device 61, and the user 7 is able to respond by receiving the call on the child device (second portable device) 62.
The location information in the conventional mobile communication system indicates the present location or the past location of the mobile terminal device of a given subscriber within a given service area. It follows that when the subscriber has moved out of the service area and wishes to respond to a call directed to the subscriber number, it was necessary that not only the basic connection service but the added call transfer service must be provided to complete the call operation.